Said Minnesota coach Rick Adelman: “They play really hard. They come at you. They’re never out of a game. They just keep competing.”

Said Rivers, now the coach of the Los Angeles Clippers: “There may be rebuilding going on, but [Celtics coach Brad Stevens] has his team competing every night. I think they’re one of the teams that, they compete every night and they can beat everybody.”

Former NBA coach Hubie Brown, now an NBA analyst for ESPN, agreed with all of the above.

“[Stevens] and his staff have a team right now that is not tremendously talented, but they play hard every night,” Brown said.

“They play to their potential on most nights. They are doing an excellent job.”

Even former Celtics forward Paul Pierce, now playing in Brooklyn, couldn’t help but comment on the subject after a recent matchup against his former team.

“They always play hard, showing that Celtic pride,” he said.

That the Celtics play hard is typically the very first thought out of the mouth of an opposing player or coach this season. But, really, how special is that attribute? Is it really that rare?

One would think that for the millions of dollars that NBA players are paid, they could at least play hard, and that for all the millions that NBA coaches are paid, they could at least get their players to play hard.

Meanwhile, back in reality . . .

Vogel explained Sunday that, contrary to public opinion, playing hard is not all that common in the NBA.

“There’s a handful of teams each year that separate themselves with their energy, how hard they play,” Vogel said.

“I think there’s probably maybe 5-8 teams that fall into that class of, ‘This team is going to play harder than you most nights.’ And I think the Celtics are one of those teams, [which is] indicative of how well they’re coached and the type of players that they have on their team. It’s a difference-maker.”

Indeed, the Celtics, who won’t play again until Saturday against Cleveland at TD Garden, have set themselves apart by their effort, which has helped them stay in games and even make late runs during games in which they trailed by double digits.

The very phrase “play hard” is also used by the Celtics in virtually every answer they provide the media. (Jared Sullinger explained a recent win thusly: “We’re just playing hard and doing the right things.”)

Stevens deflected credit for his team’s level of effort, saying it’s more the players than anything he is doing.

“I think the whole coach thing is overrated,” Stevens said. “Guys are either going to play hard or they’re not. It’s in their DNA. And that’s been what’s kept us alive and given us a chance in certain games.”

Yet Stevens’s teams at Butler University were consistently known for giving their maximum effort on a nightly basis, which helped them overachieve even playing teams that had more size or talent or both.

The Celtics, in that regard, have to rely on their effort because they have little else they can rely on in this first season of rebuilding, especially with Rajon Rondo (knee) still sidelined.

“We don’t have the dominant players that can take over the game,” said veteran swingman Gerald Wallace, whose identity throughout the NBA is tied to his almost unparalleled effort on a nightly basis. “We have to come out and compete every night, five guys playing together.”

Guard Avery Bradley, who plays as hard if not harder than any Celtic, agreed with Wallace that this team has to play hard on defense because its offense just isn’t overpowering.

“We’re a young team and when things don’t go right some young teams they don’t want to continue to give that effort the entire game,” Bradley said. “Sometimes we battle with that. That’s what kind of team we have to be, no matter how the game is going for us.

“If you’re not making shots, you should always be consistent on the defensive end. Me personally, me being one of the defensive guys on our team, I want to challenge everybody to really bring that defensive effort every single game. Because we could be a good team if we play consistent defense.”

Playing with effort on defense — another area that Stevens harps on as much as he does on playing hard — has helped the Celtics greatly in their wins, though they didn’t show much of it Sunday in a 106-79 loss to the Pacers.

Still, if all the Celtics have to their name this season is the simple fact that they play harder than their opponent on a nightly basis, it is a badge they can wear proudly, for there aren’t many teams that can say the same.

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